Production of photographic silver halide emulsions



3,ld7,43il PRGDUCTEGIN fil PEHE'EGQRAPHIQ SELVER HALlDE EM LSlGNS KarlLohnrer, Leverlrusen, and Gunter Kelli, tCologne- Stammheim, Germany,assignors to Agla Alrtiengeseilschaft, Leverkusen, Germany, acorporation of Germany No Drawing. Filed Jan. 26, 1959, Ser. No. 4,625Claims priority, applicatioinfitirmany, Jan. 27, 1959,

2 Qiainss. (Cl. Q-lld) The invention relates to the production ofphotographic silver halide emulsions.

Usually, silver halide emulsions are prepared by combining aqueoussolutions of silver nitrate and awatersoluble halide in the presence ofa protective colloid whereby silver halide is precipitated. The purposeof the protective colloid during the precipitation is to prevent theagglomeration of the silver halide grains, to iniluence the graindistribution and to control the growth of the grain and also theformation of sensitivity centres during the physical and chemicalripening.

For a long time, gelatinhas proved particularly suitable in practice asa protective colloid. It largely satisfies the photographic technicalrequirements which are demanded of a protective colloid. On the otherhand, it does however have certain disadvantages, since it is a naturalproduct, so that it is subject to certain fluctuations as regardsquality and consequently shows changing photographic properties, whichin certain circumstances cannot be detected during the processingoperations, even with highly developed testing methods. Moreover, it hasthe disadvantage that it is attacked by bacteria and is subject to achemical degradation by hydrolysis during the manufacture and storage ofthe emulsions. Consequently, numerous proposals have already been madefor replacing the gelatin by synthetic products, such for example aspolyvinyl alcohol, polyvinyl acetals, cellulose derivatives,polysaccharide derivatives, polycarboxylic acids and polycarboxylic acidamides.

It is known from United States Patent No. 1,981,102 to employpolyacrylic acid or other polymeric carboxylic acids as a binder forphotographic layers.

According to United States Patent No. 2,632,794, copolymers ofacrylamide, acrylic or methacrylic acids and acrylonitrile or methyl andvinyl ketones are used as dispersing agents for silver halide during thepreparation of photographic emulsions.

According to German patent specification No. 1,040,- 370, highlypolymeric substances with a predominant proportion of acid and nitrilegroups, more especially copolymers of acrylic acid and acrylonitrile,are recommended as binders for photographic layers. If necessary, thesepolymers can comprise a small proportion of acrylamide or vinyl alcoholunits. In spite of the many proposals, the replacement of gelatin bysynthetic substances has only been partially successful, since manyplastics do not have, to the same degree as gelatin, the protectivecolloid properties which are necessary photographically, such as forexample control of the grain size during the precipitation and physicalripening and prevention of the agglomeration of the silver halidegrains. Other plastics are only capable of limited use because theyproduce insoluble deposits with the aqueous solution of the silvernitrate.

It has now been found that these disadvantages can be avoided and silverhalide emulsions which are exccllently suitable from a photographicpoint of view can be obtained by using, as protective colloid in theprecipitation of the silver halide, film-forming copolymers of 60 to 98%by weight of methacrylamide and/or acryl- United States Patent lPatented Jan. 26, 132%5 amide, l to 38% by weight of an ester of acrylicacid or methacrylic acid with a monohydric saturated alcohol whichcontain 1 to 20, preferably 1 to 10 carbon atoms and/or a vinyl ester ofa saturated aliphatic monocarboxylic acid with 1 to 20 carbon atoms and1 to 24% of an olcfinically unsaturated organic compound containing acidgroups.

By the term saturated alcohols is to be understood alcohols which aredevoid of nonbenzenoid unsaturation, i.e., and aliphatic,cycloaliphatic, araliphatic alcohols. Especially suitable are copolymersof 65 to by Weight of methacrylamide and/or acrylamide, 5 to 34% byweight of the aforementioned ester and 1 to 15% by Weight of anolefinically unsaturated organic compound containing acid groups.

Examples of alcohols used for acrylic or methacrylic acid are:

Methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol,isononyl alcohol, cetyl alcohol, cyclohexyl alcohol, benzyl alcohol. Asexamples of the vinyl esters of a saturated aliphatic carboxylic acidwith 1 to 20 carbons, there are mentioned: vinyl acetate, vinylpropionate, vinyl butyrate and vinyl stearatec; Examples of olefinicallyunsaturated organic compounds containing acid groups are more especiallythose olefinically'unsaturated compounds which contain carboxylic,sulphonic or preparing the ester of phosphoric acid groups, such asacrylic acid, methacrylic acid, sorbic acid, maleic acid, fumaric acid,itaconic acid, citraconic acid, as well as their semi-esters with theabove cited alcohols, vinyl sulphonic acid, styrene sulphonic acid,vinyl phosphonic acid and others.

The protective colloids used according to the invention are prepared byknown polymerization methods, and preferably by polymerization in Waterin the presence of watersoluble radical formers. The aqueous .polymersolutions thus obtained can be directly used asa protective colloidsolution.

It was surprising to find that the silver halide emulsions prepared inthe presence of the protective colloidsaccording to the invention do nothave the disadvantages referred to above. They have important advantagesover the silver halide emulsions prepared with known protectivecolloids. For example, the aqueous solutions or emulsions of thecopolymers according to the invention are stable at all pH values whichare to be considered practically and do not produce with aqueous silvernitrate solutions any deposit which could disturb the processing. Thecopolymers are excellent film formers which can for example becross-linked with formaldehyde and yield elastic films. They arecompatible with gelatin and ot er natural or synthetic protectivecolloids, such as polyvinyl alcohol, polycarboxylic acid amides orpolycarboxylic acids, and consequently can also be used in combinationtherewith. The silver halide emulsions prepared with the protectivecolloids according to the invention can be quickly and quantitativelycoagulated at pH values from 3 to 4, freed from the excess salts by awashing process, and thereafter the coagulate can easily be redispersedagain by raising and lowering the pH value. The absolute concentrationof the silver halide and also the ratio between protective colloid andsilver halide can be varied within wide limits, and very highlysensitive silver halide emulsions are obtained with an extremely finegrain. The photographic materials prepared with the aid of the silverhalide emulsions according to the invention are non-fogging and aredistinguished by particularly good keeping qualities, even underunfavorable atmosphcric conditions.

For the preparation of the silver halide emulsions, the aqueoussolutions or emulsions of the protective colloid according to theinvention are supplied and the aqueous solutions of the silver salt andWater-soluble halide are sibly with the addition of other photographicauxiliaries.

The further processing step takes place in accordance with knownprocesses.

In the following examples the parts indicated are parts by Weight.

Example I 695 parts of water are placed in a stirrer-type vessel and72.5 parts of methacrylamide, 25 parts of a a ueous solution ofacrylamide, 22.5 parts of methyl acrylate and 2.5 parts of methacrylicacid are introduced 7 ,and homogeneously mixed while passing nitrogenover the mixture. The mixture is then heated to 75- C. and polymerizedby adding 0.3 part of potassium persulphate. After 8 hours, theviscosity has risen considerably and a substantially 12% polymersolution is obtained.

19 parts of potassium bromide and 0.5 part of potassium iodide are nowadded to a solution of 400 parts of "Water and 100 parts of thecopolymer solution and themixture is heated to 40 C. A cold solution ofparts of silver nitrate dissolved in 150 parts of Water,

to which had been added 25 parts of ammonia water with a density of0.91, is then poured into the said mixture "over a period of 1 minute.The mixture is digested for minutes at C. and'coagulation is thereaftereffected by adding 52 parts of dilute sulfuric acid (density Thesupernatant salt solution is decanted off, 7 the coagulate is washedtwice with 1000 parts of water and is finally redispersed in 200 par-tsof water to which 1 part of sodium carbonate had been added.

It is immediately subjected, with the addition of 30 g. of gelatin, to achemical ripening at C. for to 80 minutes. 011 completing the ripening,the emulsion is cast by known methods on to a layer support.

Example 2 As described in Example 1, 620 parts of water are providedand'40 parts of methacrylamide, 310 parts of a 10% aqueous solution ofacrylamide, 25 parts of vinyl acetate and Sparts of a 50% aqueoussolution of acrylic acid are introduced and polymerization carried outas described therein. A substantially 10% aqueous polymer 3 solution isobtained.

The processing to form photographic silver halide emulsion layers takesplace as described in Example 1.

Example 3 As described in Example 1, 716 parts of water are provided and78 parts of methacrylamide, 15 parts of ethyl acrylate, 3 parts of vinylpropionate and 8 parts 'of a 50% aqueous solution of acrylic acid areintroduced and polme'rization takes place as described therein. Asubstantially 12% aqueous polymer solution is obtained.

The processing to form photographic silves halide emulsion layers takesplace as described in Example 1.

Example 4 are now simultaneously poured within 5 minutes at C. into asolution of 50 parts of the copolymer solution in 300 parts of water.The emulsion is thereafter subjected to a physical ripening for 30minutes, and after adding parts of gelatin with a powerful ripeningaction, chemical ripening takes place at the same temperature over aperiod lasting 30 minutes. The emulsion is then cooled, provided withthe necessary casting additives, such as optical sensitizer, wettingagent and hardening agent and cast. The gelatin can also be replaced byanother'carrier colloid to which has been added the necessary quantityof chemical sensitizers.

Example 5 As described in Example 1, 716 parts of water are provided and79.5 parts of methacrylamide, 165 parts of ethyl acrylate and 8 parts ofa 50% aqueous solution of acrylic acid are introduced and polymerizationis peracid are added, the silver halide coagulating and settling veryquickly. The precipitate is freed from the supernatant salt solution,washed several times with slightly acidified water, again redispersedwith dilute sodium hyocyanate, thiosinamine, and sodium thiosulphateuAfter completing the ripening, the emulsion is cast by known 1 methodson to a supporting layer.

We claim:

1. In av process for the production of photographic silver halideemulsions by precipitating a silver halide in an aqueous mediumcontaining a protective colloid, coagulating said emulsion to obtain acoagulate containing said protective colloid and said precipitatedsilver halide and redispersing said coagulate, the improvement accordingto which the silverhalide is precipitated in an aqueous mediumcontaining as the only protective colloid a film-forming copolymerconsisting essentially of (1) 65 to by weight of a member of the groupconsisting of methacrylamide, acrylamide and mixture thereof, (2) 5 to34% by weight of a monomer of the group consisting of vinyl esters of asaturated aliphatic monocarboxylic acids containing from 1 to 20 carbonatoms, esters of acids of the group consisting of acrylic acid andmethacrylic acid with monohydric saturated alcohols containing from 1 to20 carbon atoms and (3) 1 to 15% by weight of an olefinicallyunsaturated organic compound containing acid groups selected from thegroup consisting of acrylic acid, methacrylic acid, sorbic acid, maleicacid, fumaric acid, itaconic acid, citraconic acid, vinyl sulfonic acid,styrene sulfonic acid and vinyl phosphonic acid.

2. A process as defined in claim 1, in which the filmforming copolymeris a copolymer formed from approximately 72.5 parts of methacrylamide,2.5 parts of acry1- amide, 22.5 parts of methyl acrylate, and 2.5 partsof methacrylic acid, all parts being by weight.

References Cited in the file of this patent UNITED STATES PATENTS2,461,023 Barnes et a1. Feb. 8, 1949 2,611,763 Jones Sept. 23, 19522,811,494 Smith et a1 Oct. 29, 1957

